Disease-modifying therapies with distinct mechanisms of action are now available to treat autoimmune diseases. Several agents have shown the ability to delay onset of Type I Diabetes (T1D), but only in a fraction of patients and for a limited period of time. Why these disparate agents show such similar clinical effects remains unknown, but their limited effectiveness, high cost and potential for undesirable side effects have limited their usefulness in T1D. By better selecting patients for treatment, the likelihood of treatment success, patient well-being, and cost-effectiveness may improve. We are using cutting edge systems biology approaches to identify cellular and molecular markers characterizing the preservation of beta cell function in newly diagnosed subjects with T1D (non-progressors). In preliminary studies, we used RNA sequencing analysis (RNAseq) to identify a gene expression signature of EOMES-positive cells in whole blood samples from non-progressors after teplizumab treatment. With the current proposal, we request funding to expand our initial studies by pursuing three molecular profiling-related approaches: Identify unique and shared molecular/cellular signatures distinguishing T1D non-progressors from progressors following treatment. We will use RNAseq analysis to identify whole blood molecular signatures in subjects treated with several agents that protect beta cell function, including abatacept, rituximab, and alefacept. Identify molecular/cellular signatures distinguishing T1D non-progressors from progressors during the natural history of T1D after diagnosis. We will use RNAseq analysis to identify signatures in whole blood of T1D subjects that naturally show preserved beta cell function, even without treatment. Signatures from the first two approaches will be compared with our teplizumab signature to determine whether each is unique or treatment-specific. Identify cell types accumulating in non-progressor teplizumab-treated patients from the AbATE study and generate hypotheses as to their function. We will perform flow cytometry and single cell transcriptome profiling studies to characterize the EOMES-positive cells identified in our preliminary studies. Together, we expect these studies to yield improved understanding of immune aspects of beta cell preservation in T1D. We also anticipate identifying new biomarkers, better strategies for patient selection and more rational combination therapies for T1D.